In known arrangements of this character, it has been found that as the contamination increases in the air filter which is used in the suction system, for example where there is poor maintenance, the reduced pressure in the suction system of the engine becomes particularly severe and affects the pressure compensation very unfavorably despite interposed valves. In addition to this it has been found that even the pulsations in the quantities of discharge gases in the crankcase itself cannot be trapped by known arrangements. Again, irregular and uncontrollable flows or fluctuations of quantities of gas occur in the connection conduit and these frequently drag oil from the crankcase into the suction system to cause familiar disadvantageous phenomena. Moreover, the pressure is frequently reduced to an excessive extent and this permits incursion of dust and contaminant particles from the exterior through small gaps in the sealing means of the crankcase. These intruding particles cause considerable damage to the sliding and control surfaces on moving parts in the crankcase and produce excessive wear of these elements. This notably reduces the length of life of the engine.
It is an object of the invention to remove these shortcomings and to relieve the control valve in the connection conduit to a maximum degree of these detrimental effects. This problem is solved in the present invention by the fact that the control valve is so arranged that it is exposed on the one hand to the pressure in the crankcase and, on the other hand, to the pressure prevailing in an operating chamber which is separate from the connection conduit and communicates with atmosphere through an auxiliary conduit. By these means fluctuations in underpressure at the suction side of the engine cannot have any detrimental effect on the control valve. Moreover, the pressure compensation will be regulated in dependence only on the pressure level in the crankcase.
In a preferred embodiment of the invention, the arrangement is such that the operating chamber is formed directly in the connection conduit by a shut-off member and at the same time an overflow connection is provided under the control of the valve to make or interrupt the connection between the crankcase and the suction pipe. Advantageously, the overflow connection comprises a tubular jacket which encloses and is spaced from the connection conduit in the zone of the operating chamber, and transverse holes which are arranged fore and aft of the operating chamber.
It is particularly advantageous when the control valve is in the form of a piston which, in its rest position, closes the transverse holes which permit entry of the overflow gases into the tubular jacket. The connection conduit can be approximately vertical and the piston held in its rest position by gravity. In a further useful arrangement, the piston is loaded by an adjustable return spring. By these means, the pressure level in the crankcase can be maintained either by appropriate choice of the piston weight or by appropriate adjustment of the power of the return spring.
It is to be noted that the control valve may be in the form of a ball valve .